RICHARDS: MITOSIS IN PODOPHYLLUM. 93 



it points toward the view that while the cell is the unit of 

 structure the chromosome is the unit of potentiality, and that 

 the chromosomes themselves may all differ in structure and, if 

 in structure, also in potentiality. 



An interesting problem concerning these root-tip cells is the 

 relation of the cells to the entire tissue and the cytological 

 processes of later stages of embryonic growth. Material for 

 this study is not at hand at this time, but I hope to be able to 

 trace out these processes at some subsequent period. 



BIBLIOGRAPHY. 



1. D. M. MOTTIER. Fecundation in Plants, Carnegie Institute, 1904. 



2. J. H. SCHAFFNER. Karyokinesis in Root-tips of Allium cepa, Botanical 



Gazette, 36:226. 



3. Adolph Hof. Botanisches Centralblat, LXXVI, 65, 113, 166, 221. 



4. Eduard Strasburger. Ueber Plasmaverbindungen pflanzlicher Zellen, 



Jahrbiicher fiii- wissenschaftliche Botanik, 1900. 



5. Haberlandt. Function und Lage des Zellkernes — Jena, 1887. 



NOTE. 



The drawings of the Podophyllum root-tips were all made with the aid 

 of a camera lucida (B. & L.) A C. Reichert Mo objective was used and 

 with it a B. & L. i/^-inch ocular for the larger figures and a %-inch for the 

 smaller, making a magnification of 2466 and 2000 diameters, respectively. 



Figures 9, 13, 14, 15, 16, 18, 20, 22, 23, 24, were made from material 

 stained with the Flemming three-color method. The others were made 

 from sections stained with the iron-haematoxylin method. 



2-Univ. Sci. Bull.. Vol. V. No. 6. 



